The objectives of this study are 1) to biochemically identify the specific gene products associated with the HLA-D region that contribute to the susceptibility of Insulin Dependent Diabetes (IDD) and 2) to study the expression of the biochemically identified forms, as IDD specific on transfectant cells. This will be accomplished by using cryopreserved cells and sera from a large number of patients that have been collected and typed for HLA class I and II antigens. In addition, a panel of 23B-lymphoid cell lines (B-LCL) derived from 10 families will be utilized. The study will consist of: 1) Characterization of HLA-DR and DO alpha and beta subunits from B-LCL derived from IDD patient carrying the HLA-DR3 and/or DR4 haplotypes by two dimensional polyacrylamide gel electrophoresis (2D-PAGE), high pressure liquid chromatography (HPLC) and restriction fragment analysis of the DNA (RFLP). 2) Identification of combinatorial (hybrid) DQ antigens forming unique Ia determinants generated as a result of the association of the alpha and beta chains from two haplotypes which can function as restriction elements conferring susceptibility to IDD. 3) Identification of alloantibodies reactive with IDD associated antigens in the sera of multiparous mothers of IDD patients. 4) Isolation of the genes coding for the molecular forms of DR or DO that the biochemical studies indicated to be IDD specific and generation of transfectants expressing these genes. Information generated from this study will help to identify molecular forms more frequently seen among IDD patients and indirectly to use them as markers for identifying those at risk. The transfectants generated will provide an excellent system for studying the genetics of the susceptibility to IDD and will also constitute a model for other Ia associated diseases.